The disclosure of Japanese Patent Application No. 2000-060111 filed on Mar. 6, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a fuel cell that has a stack formed by stacking a plurality of collector plates and a plurality of electrolyte films provided with reaction electrodes, supply manifolds formed in the stack for distributing and supplying reaction gasses to gas passages formed between the electrolyte films and the collector plates, and discharge manifolds into which reaction gases from the gas passages are discharged. The invention also relates to a collector plate of a fuel cell, the collector plate having gas passages, and supply holes and discharge holes for forming the manifolds.
2. Description of the Related Art
A fuel cell has a stack body having a stack structure formed by stacking unit cells. Each unit cell is made up of an electrolyte film carrying reaction electrodes on its both side surfaces, and current collector plates placed at opposite sides of the electrolyte film. A surface of each collector plate facing the adjacent electrolyte film has gas passages for conveying reaction gasses, such as a fuel gas, an oxidant gas, or the like. Inside the stack, supply manifolds and discharge manifolds extend in the stacking direction. The reaction gasses are supplied and discharged between the manifolds and the gas passages of each collector plate. Each manifold is formed as a passage by connecting holes in series that are formed in the collector plates as described in, for example, Japanese Patent Application Laid-Open No. HEI 10-106594. Each collector plate has a plurality of holes that are formed at predetermined positions corresponding to the manifolds.
In this fuel cell, the reaction gasses, supplied from the inlets of the manifolds thereinto, are distributed and supplied into the gas passages of each unit cell via supply manifold-forming supply holes that are formed in the collector plates. After being distributed and supplied into the gas passages, the reaction gasses flow through the gas passages, and then are discharged into the discharge manifolds via discharge manifold-forming discharge holes that are formed in the collector plates. By thus causing the reaction gasses to flow through the gas passages of each unit cell, an electromotive force is generated between the reaction electrodes of each unit cell in an electrochemical reaction manner.
Thus, in the fuel cell, an electromotive force is extracted by causing the reaction gasses to flow through the gas passages of the collector plates. Therefore, in order to achieve a desired electric power generating efficiency in the fuel cell, it is desirable to appropriately control the amount of flow of the reaction gasses and the distribution thereof in the gas passages.
However, in the aforementioned fuel cell in which each reaction gas is supplied and discharged between the corresponding gas passages and the manifolds common to those gas passages, there is an unignorable problem as follows, regarding the amount of flow of each reaction gas and the distribution thereof.
The amount of flow of each reaction gas tends to decrease with increases in the distance of a unit cell from the inlet of the supply manifold. Therefore, whereas sufficient amounts of the reaction gasses are supplied to unit cells that are relatively close to the inlets of the supply manifolds, the amounts of the reaction gasses supplied into the gas passages of unit cells that are relatively remote from the inlets of the supply manifolds become insufficient, and therefore the electromotive forces generated by those unit cells become relatively low. Thus, in the fuel cell in accordance with the relative art, the distribution of each reaction gas to the gas passages is biased, so that some of the unit cells fail to generate a desired electromotive force. Therefore, a reduction in power generating efficiency is inevitable.
Accordingly, it is an object of the invention to provide a fuel cell and a collector plate thereof that are able to improve the characteristic of reaction gas distribution to the gas passages in the fuel cell.
In order to achieve the aforementioned and other objects, a collector plate of a fuel cell in accordance with an aspect of the invention includes a gas passage formed in at least one surface, a supply hole for distributing and supplying a reaction gas into the gas passage, and a discharge hole for discharging the reaction gas from the gas passage. An opening area of the discharge hole is set greater than an opening area of the supply hole.
In a fuel cell, the reaction gas supplied from the supply hole into the gas passage of each collector plate is discharged via the discharge hole. In this process, the discharge hole tends to function as a constriction, and tends to restrict the flow of the reaction gas. In general, the gas passage of a collector plate located near a supply manifold is supplied with the reaction gas at a relatively high pressure from the supply manifold, so that the reaction gas is relatively rapidly discharged via the discharge hole although the flow is restricted by the discharge hole.
The gas passage of a collector plate located remotely from an inlet of the supply manifold, on the other hand, is supplied with the reaction gas at a relatively reduced pressure. In such a gas passage, therefore, the influence of the constricting effect of the discharge hole becomes great, so that the reaction gas becomes less apt to be discharged. As a result, the amount of the reaction gas supplied to the gas passage via the supply hole becomes less in a collector plate located remotely from the inlet of the supply manifold than in a collector plate located near the inlet.
In the above-described aspect of the invention, however, the restriction on flow by the constricting effect of the discharge hole is reduced, so that the reaction gas can be promptly discharged from the gas passage via the discharge hole. Therefore, even in the case of a collector plate disposed remote from the inlet of the supply manifold, at least a predetermined amount of the reaction gas can be caused to flow through the collector plate. Thus, the bias of distribution of the reaction gas to the gas passages of the unit cells that constitute a fuel cell can be reduced, and the distribution characteristic can be improved.